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Full text of "Text Book Of Mechanical Engineering"

216                         General Directions.

may be made, although all figured the same on the drawings,
Clearance size is for bolt holes, so that the bolt may drop in
freely; tapping size is that at the bottom of the screw-thread ; and
gauge size is divided into 'working fit7 and 'driving fit/ the first
having both pairs made to gauge, and the second having its socket
to gauge and the pin callipered to suit the plug gauge.

As regards the drawings; these are classified as previously
described, but we shall further give each article a number in
Roman letters; and in nearly all cases the drawing itself will be
indicated by the letter A, while the various operations take the
succeeding letters of the alphabet. At the close of the descrip-
tions a e general arrangement' or complete drawing of the engine              ^
will be given, and we shall thus have followed in nearly every *
particular the practical methods of the workshop. One sheet              I
is omitted, that representing a collection of all the bolts and
studs to be used on the engine. This has been thought unneces-
sary, as the capstan lathe has already been described where these
parts are tooled. It may further be mentioned that there are
always more ways than one of performing the various operations,
both as regards sequence and the tools used, and it may also
follow that each method is equally good; in many cases, too,
where the marking-table is mentioned in our descriptions, it might
be found more convenient to scribe the work while in the machine.

I. Regulator Lever (Fig. 228).—This must first be set
upon edge, on blocks, as at B, until level; and a centre line
he scribed all round it. The circles may be struck, just to see
if the stuff c holds up/ and the length of the handle marked
off from these. Now punch all the five centres. (A method of
centering with scribing block by laying the lever successively on
its four sides and scribing any convenient height is shewn at D,)
Lay the lever next on its side (c), and pack up until the centres
are quite horizontal, as measured with scriber. Then scribe the
centre line all round, and mark at the same time the thickness
of the bossesf and of the lever itself, as measured from this
centre. Next put in the lathe, and square-centre; then turn and
polish the handle. Remove and clamp to the table of a shaping
machine, so as to shape across the flat parts; then clamp on .the
lathe face plate as shewn at E, for the purpose of drilling the